In order to ensure the accuracy in controlling output torque of internal combustion engines and the quantity of exhaust emissions therefrom, it is essential to control a fuel injection mode such as the quantity of fuel to be sprayed from a fuel injector or the injection timing at which the fuel injector starts to spray the fuel. For controlling such a fuel injection mode, there have been proposed techniques for sensing a change in pressure of the fuel resulting from spraying thereof from the fuel injector.
For instance, the time when the pressure of the fuel begins to drop due to the spraying thereof from the fuel injector may be used to determine an actual injection timing at which the fuel has been sprayed actually. The amount of drop in pressure of the fuel arising from the spraying thereof may be used to determine the quantity of fuel sprayed actually from the fuel injector. The detection of such an actual fuel injection mode ensures the accuracy in controlling the fuel injection mode based on a detected value.
When such a change in pressure of the fuel is measured by a fuel pressure sensor (i.e., a rail pressure sensor) installed directly in a common rail (i.e., an accumulator), it will be absorbed within the common rail, thus resulting in a decrease in accuracy in determining such a pressure change. In the invention, as taught in the patent document 1, the fuel pressure sensor is disposed in a joint between the common rail and a high-pressure pipe through which the fuel is delivered from the common rail to the fuel injection valve to measure the change in pressure of the fuel before it is absorbed within the common rail.    Patent Document 1: Japanese Patent First Publication No. 2000-265892